1. Field of the Invention
The present invention relates to improvements of a perpendicular magnetic recording medium used for a magnetic recording and/or a reproducing apparatus and a manufacturing method for the same, and it particularly relates to a perpendicular magnetic recording medium suitable to a high density magnetic recording.
2. Description of the Related Art
Presently, a Co--Or alloy is widely employed in a perpendicular magnetic recording medium as a magnetic thin film for magnetic recording. Such a perpendicular magnetic recording medium is constructed by forming the magnetic thin film, for instance, made of the Co--Cr alloy on one side of a non-magnetic base, using a surface treatment technique such as a sputtering method, a vacuum evaporation method or a plating method among which, however, a dry process such as the sputtering method and the vacuum evaporation method become a main current of the surface treatment technique because of a high corrosion resistance characteristic and facility in controlling dust and forming conditions of the magnetic thin film compared with a wet process such as the plating method.
In this dry process, the non-magnetic base requires a high sputtering temperature about 200.degree. C. to obtain an acceptable Co--Cr alloy thin film having, for instance, a high coercive force Hc(.perp.) and good crystalline structure. Therefore, the non-magnetic base requires a heatproof material, for instance, such as Ni, NiP, glass, alumitc (aluminum Oxide clad material) or high heat resistance resin, which poses a problem that these materials are too expensive to use. Further, there is a drawback that the magnetic thin film obtained by the dry process has a large stiffness and a large internal stress, so that the magnetic thin film is difficult to be used together with a flexible non-magnetic base. Furthermore, there are another drawbacks that Cr used in the sputtering process as an evaporation source is harmful for the health, and Co used in the same process is very expensive.
Japanese Laid Open Patent Application No. 193125/1985 and Japanese Laid Open Patent Application No. 84005/1988 disclose an employment of a Fe--Nd alloy thin film instead of a Co--Cr alloy thin film in a perpendicular magnetic medium to eliminate the above drawbacks.
In the above prior arts, the Fe--Nd alloy thin film is formed on a non-magnetic base by the sputtering method at a sputtering temperature below 100.degree. C., however, the Fe--Nd alloy thin film obtained has a low corrosion resistance and an amorphous structure, which poses a problem that the Fe--Nd alloy thin film is not practical because of magnetic characteristics change with a time lapse and of a low Curie point.